A ball screw device is provided with a nut having an inner peripheral surface in which a helical screw groove is formed, a screw shaft having an outer peripheral surface in which a helical screw groove is formed, and a plurality of rolling members that are arranged between the screw groove of the nut and the screw groove of the screw shaft. The nut is formed with an endless circulation path connecting one end of the screw groove of the nut and another end thereof, and a rolling member that rolls and reaches the one end of the screw groove circulates toward the other end thereof through the endless circulation path. According to such structure, in the ball screw device, the nut is capable of being linearly reciprocally moved along the axial direction of the screw shaft according to the rotation of the screw shaft.
In the ball screw device of the structure mentioned above, the nut is moved along the screw shaft having long scale, and accordingly, if the nut is moved in a state in which foreign materials such as work cut chip, or dust and dirt adhere to the screw shaft, the rolling member rolling in the rolling member rolling groove bites such foreign material, which may deteriorate moving performance of the nut rolling in the rolling member rolling groove in an early stage of operation. Because of such reason, in an actual use of the ball screw device, it is general to adopt a structure in which seal members for sealing clearances or gaps between the nut and the screw shaft at both the end portions in the axial direction of the nut is arranged to thereby remove the foreign materials adhering to the screw shaft by the seal members in association with the movement of the nut.
For example, as described in the following Patent Document 1, there is known a ball screw device which is provided with a nut having an inner peripheral surface in which a screw groove is formed, a screw shaft having an outer peripheral surface in which a screw groove is formed, balls arranged between track grooves formed by the screw groove of the nut and the screw groove of the screw shaft, and a plurality of ring-shaped seal members. Each of the seal members has a body portion having an edge portion fixed to the nut and a lip portion contacting the outer peripheral surface of the screw shaft and the screw groove in an elastically deformable manner, and a lubricant containing member is disposed between the adjacent seal members.
According to the ball screw device of the structure mentioned above, since the lubricant containing member is disposed between the adjacent seal members, lubrication can be performed to the lip portions of both the seal members without increasing torque which may be caused when grease is applied, and high sealing performance can be ensured.